Pulse-shift measurement: a direct observation of radical pair dynamics in a micelle

Abstract

Abstraet. The hydrogen abstraction reactions of benzophenone in a micellar solution in the absence and presente of 1,4-cyclohexadiene are compared with time-resolved electron spin resonance (ESR) and optically detected (OD) ESR. "Pulse shift" measurement by OD-ESR, which observes the effect of a resonant microwave pulse at different delay times after laser excitation, reveals that the lifetime of the radical pair becomes much shorter in the presence of 1,4-cyclohexadiene. This explains the change of chemically induced dynamic electron polarization from spin-correlated radical pair polarization in the absence of 1,4-cyclohexadiene to conventional E'/A polarization in its presence. The rate constants determined by this technique indicate that the escaping rate of cyclohexadienyl radical is ten times Iarger than those of alkyI and benzophenone ketyl radicals.

Direct observation of f-pair magnetic field effects and time-dependence of radical pair composition using rapidly switched magnetic fields and time-resolved infrared methods

“…is analogous to the microwave pulse position technique applied in ODESR spectroscopy. 29 The size of the integrated signal depends on the number of geminate RPs during the application of the magnetic field pulse and so is a powerful technique for measuring the lifetime of these species. The pulsed magnetic field method differs from ODESR based methods by allowing the RP lifetime to be measured in zero field (in the approach described here) or alternatively in weak magnetic fields by applying a continuous magnetic field and rapidly switching it off for a short duration at variable times relative to the excitation laser pulse.…”